And, US 7,905,805, issued to Shimano on March 15, 2011, highlights some of the advantages of placing the derailleur and chain tensioner on the chainstay:

Furthermore, the location of the tension device 250 at about mid-way between the gear changing device 232 and the front sprocket of the bicycle ensures that the expanse of unsupported drive chain 218 [] is minimized, as compared to other designs []. The above factors beneficially reduce the flopping movement [] of the chain 218 during the impact and absorption of the impact force, as compared to other designs.

In addition to the above benefits, the rear derailleur device 230 of the embodiment of the present invention allows for a reduction in the size and weight of the device adjacent the rear sprocket 216. For example, note that the gear changing device 232 is smaller in size and weight than the rear derailleur 330 in FIG. 6A. Additionally, the rear derailleur device 230 of the embodiment of the present invention reduces or prevents entanglement of the drive chain with the gear changing device 232 when the tension device 250 pivots due to impact.

I admit that I’ve been fortunate to never have a derailleur go into my rear wheel, but I’ve seen it and the frustration it’s caused. Could the chainstay derailleur and chain tensioner be the solution?

Application: US 14/066,943
Application Status: Response Filed on March 12, 2015, Published as US 2014-0357437
Assignee: Shimano, Inc.
Related Patents/Applications: Continuation in Part of US 13/910,043, under non-final rejection and published as US 2014-0357436.

As much as I love all bikes, I’m a mountain biker at heart. And, I’m excited to see Shimano’s Di2 coming to XTR. Synchro-Shift operates both the front and rear derailleurs in response to input from one shifter. Or, another way, the rider only says, “I need a higher/lower gear,” and Synchro-Shift says, “Okay. We’ll move the front and rear derailleurs like this for you.” It’s like having a 1x drivetrain but with a front derailleur that you don’t have to mess with.

Last November, Shimano received US 8,882,122 drawn to this technology. The illustrated example provided in the patent is only for a 3×10 drivetrain, but you can see the similarities. FIG. 4 of the patent compared to 2:10 of the video: